DoxyPEP reduces chlamydia and syphilis rates in routine care

A new study has found that rates of chlamydia and syphilis plummet among people prescribed doxycycline for sexually transmitted infection prevention in routine clinical care.

The study was led by the Harvard Pilgrim Health Care Institute with collaborators from Kaiser Permanente Northern California, Kaiser Permanente Mid-Atlantic States, and Kaiser Permanente Georgia. It was published on January 6 in JAMA Internal Medicine.

DoxyPEP is a new strategy for preventing STIs that involves taking a dose of doxycycline, a common and well-tolerated antibiotic medication, within 72 hours of sex. Clinical trials have shown that using doxyPEP greatly reduces the risk of acquiring bacterial STIs, particularly chlamydia and syphilis, among people assigned male sex at birth. However, few studies have assessed whether use of doxyPEP reduces STIs when prescribed in routine care.

Interventions that are effective in clinical trials don't always end up working in real-world settings, where people tend to face more barriers to consistent medication use. We were excited to see that doxyPEP users in our study experienced declines in chlamydia and syphilis comparable to those observed in clinical trials."

Michael Traeger, PhD, research fellow at Harvard Pilgrim Health Care Institute and lead author of the study

In October 2022, San Francisco became the first jurisdiction to issue guidelines recommending that doxyPEP be offered to gay and bisexual men and transgender women at risk of STIs. Kaiser Permanente Northern California began offering doxyPEP to people using HIV PrEP, or preexposure prophylaxis, shortly thereafter, in November 2022.

The new study, which examined the largest cohort of doxyPEP recipients reported globally to date, used pharmacy data to determine which HIV PrEP users in Kaiser Permanente Northern California filled prescriptions for doxyPEP. Demand was high: of nearly 12,000 HIV PrEP users, almost one in five – 2,253 people – received doxyPEP within its first year of availability. The vast majority of people prescribed doxyPEP were assigned male sex at birth, and doxyPEP users were racially and ethnically similar to the overall population of HIV PrEP users.

The researchers then looked at STI test results before and after doxyPEP initiation to understand how doxyPEP use may have affected risk of acquiring STIs. They found that STI incidence declined by 79% for chlamydia, 80% for syphilis, and 12% for gonorrhea.

"Since we started offering doxyPEP to our patients, our clinicians have seen a marked decline in both positive STI test results and the number of patients needing treatment after an STI exposure," said study co-author Jonathan Volk, MD, MPH, an infectious disease specialist with The Permanente Medical Group. "But the reduction in gonorrhea in our study was modest, underscoring the importance of regular STI testing for patients using doxyPEP."

"Rising syphilis rates, including more cases of congenital syphilis, highlight the urgent need for innovative tools like doxyPEP," added co-author Michael Silverberg, PhD, MPH, an HIV epidemiologist with the Kaiser Permanente Division of Research.

"We know there are important questions that still need to be answered about doxyPEP, including its effects on antimicrobial resistance," said Julia Marcus, PhD, Harvard Medical School associate professor of population medicine at the Harvard Pilgrim Health Care Institute and senior author of the study. "In the meantime, our study suggests that broader implementation of doxyPEP could have tremendous benefits for reducing STI transmission and improving sexual health."